Pneumatic switch



Patented Oct. 19, 1937 UNITED STATES PATENT OFFICE PNEUMATIC SWITCH Application September 14, 1935, SerialNo. 40,521

5 Claims.

This invention relates to pneumatic switches, and more particularly to pneumatic switches for use in connection with brake equipments for railway trains and traction vehicles.

Pneumatic switches are a familiar part of brake equipments embodying electrical features. Since the brakes on trains and traction vehicles are a part of the safety equipment, each part of the brake equipment must provide a high degree of reliability. And this reliability must be present even under the most rigorous service experienced in railway and traction vehicle operation.

It is a principalobject of the present invention to provide a pneumatic switch which will operate with a high degree of reliability under the most rigorous service required of brake equipments for trains and traction vehicles.

'It is a further object of the invention to provide a pneumatic switch which can be manufactured at a reasonable cost, which is simple in operation, and which will require a minimum of maintenance.

A further objectof the invention is to provide a pneumatic switch which will be snap-acting in character, and which will not introduce disturbing factors in the normal operation of the pneumatic portions of a brake equipment with which the switch is associated.

Other objects of the invention, dealing with specific constructions, special features, and special arrangements of parts, will be apparent from the following description, which is taken in connection with the attached drawing wherein,

Fig. 1 is a sectional View in elevation of one embodiment of the invention.

Fig. 2 is a view along the line 2-2 of Fig. 1.

Fig. 3 is a view in perspective of a contact employed in the embodiment of Fig. 1.

Fig. 4 is a fragmentary view showing a modification of the embodiment of Fig. 1.

Fig. '5 is another fragmentary view showing still another modification of the embodiment of Fig. 1.

Considering now the embodiment shown in Figs. 1 and 2, I haveshown two stationary contacts I connected by an L-shaped bridging contact I I, which is carried by a lever I2 adapted to be rocked by a piston I3 disposed in a piston chamber I 4'.

The two stationary contacts I0 are preferably of brass, copper, or an alloy having a relatively high degree of conductivity and are preferably secured to an insulating block I5 by means of flat headed machine screws I6, A reinforcing member I! preferably overlies each of the contact members I0 so as to more firmly hold the contact member against the block I5 and to provide a suitable contact base for a terminal I8 attached to one of two conductors IS. A machine screw is provided to secure the terminal I8 to the overlying member I! and contact I0.

Each of the contacts I0 is preferably disposed in a recess or slot 2I in the insulating block I5, so as to prevent movement of the contact I0 out of alignment with the movable contact II. Each contact I0 is also provided with a contact tip 24 secured thereto and having a wedgeshaped configuration, as is shown more clearly in Fig. 3.

The insulating block I5 is preferably secured by bolts and nuts 25 to a bracket 26, which in turn is secured by machine screws 21 to a plate 28. The plate 28 is secured to a base member 29, preferably a casting, by means of machine screws 30.

The lever I2 is rotatably disposed on a pin 32 carried by the base member 29. The upper end of the lever I2 is provided with a flat portion 33 to which is secured another insulating block 34, which carries the L-shaped bridging contact II.

The insulating block 34 may be secured to the portion 33 by a machine screw 35, while the bridging contact II may be secured to the insulating block by a rivet or screw 36, with a collar or spacer 31 interposed between so that heat generated in the bridging contact will not be transmitted directly to the insulating block.

Projecting from the lever I2 above its fulcrum point 32 is an arm 38 having an aperture 39 in which is hooked one end of a coil spring 40. The other end of the coil spring 40 loops around a reduced portion 4| of a stud 42 screwed into the based member 29. The spring 40 therefore urges rotation of the lever I2 in a counterclockwise direction, so as to urge the bridging contact II into engagement with the two stationary contact tips 24.

The lower end of the lever I2 is bifurcated and has secured between the bifurcations the head of a pin 44 which is slidably disposed in the bore of a sleeve 45 forming the stem of the piston I3. When there is no pressure in the piston chamber I4, the pin 44 is actuated by spring 40 into the sleeve 45 to bias the piston I3 to its extreme right hand position.

In the extreme right hand position of piston I3, a gasket 46 carried thereby is in sealing engagement with an annular seat rib ll. The gasket v II) is held in place by a snap ring 48.

piston chamber I4 to a degree sufilcient to overcome the opposing force exerted by spring 40,

piston I3 is actuatedlto the left until a seat rib '49 thereon seals againsta gasket 50 interposed,

between cap forming the piston chamber M,

and the base member 29. When the piston l3 has thus reached its extreme left hand position the lever I2 will have been rotated to adegree such that L-shaped contact H will have disen gaged from the two contact tips 24, and the connection therebetween thus interrupted.

The piston i3 is provided'with a restricted port 52 connecting the chambers on either side of the,

piston, and located outside of the seat rib 49. The purpose of this arrangement will appear more fully hereinafter.

Fluid undl'er 'pressure may besupplied to the piston chamber l4 byway of pipe 53, and this pipe may be connected to any one of the different pipes employed in a fluid pressure brake system, as for example the straight air pipe, the

sandingflpipe, or the like. l

The switch device is preferably fully enclosed by the provision of suitable casing members. The lowerportion of the switch may be enclosed by a casing member 56 secured in place to the base member 29 by screws 57, while the upper portion of the switch may be enclosed by an assemblage of casing members 58 and 59, secured or together by spot welding or other means, as

shown. in *Figs. '1 and 2. It will be noted'that V the member 59 forms the leftand right end walls and also the top wall of thecasing. In addition, the lower edge of the right end wall formed by this member is slit and turned inwardly so as to'form toes 6B. for receivingthe right, end

of the plate 28. V l

V The left end wall portion" of the member 59 has secured thereto a small bracket 61 to which 'is'fastened an almost-circular ring 62 adapted .to

be elongated by hand pressure in a vertical di rection and then snapped into a recess 63in a lug 64 secured to the plate 28, so as to thus hold the casing formed by themembers 5E and 59. in'place. To remove the ring 62 from thesl'ot,

63' a releasing finger 65 is moved downwardly and the ring thus snapped fromithe recess so that the casing members-58 and 59 may be removed, and entrance to the contact mechanism and'tfi are in place the contact mechanism is wholly enclosed, but when they are removed there is free access to the contact mec anism from all sides so. that inspection :or repairs may i be readily made.

If the conductors I 9 are normally encased in a conduit 66, this conduitmay be screwed into a boss Bl provided for thatpurpose, and theconductors thus enter the casing'of the. switch de- 1 vice without exposure.

. The switch device may be secured to a mounting surface by means of. a bracketmember 68' V l which is securedto the base member 29 by rivets Qwamn. the casing of the switch device at arc shields'lll maybe provided to shield the cas-' ing from ny arcing produced by openings of 'the'switch contacts. Theseshields Iare preferably 'of some. asbestos composition, so as to withstand considerable heat. V

a While in the arrangement described I only. two

7 stationary contacts it] have been shown, areature of the invention is that'a number of sets of such contacts'maybe arranged "upon a suit- 2,096,492 When fluid under pressureis supplied to the able insulating block and one or more bridging contacts ll provided to selectively bridge these contacts in response to operation of the one piston I3. For example, there may be four stationary contacts l0, and two bridging contacts It so spaced and supported by an insulating blockI 34 that one bridging contact H bridges two of the stationary contacts l6 while the other bridg ing contact ll bridges the two remaining stationary contacts. In this manner two different circuits may be controlled. In a like manner, any number of sets of contacts may be controlled.

In operation, the spring lllnormally biases the lever l2 to a position where the bridging contact II engages and bridges the two contact tips 24'.

. Due to the particular form of the contact tips 24 and the bridging contact ll employed, as

shown, if there should be appreciable wear of the piston gasket it against the seat rib 41, the

contact area will not be appreciably changed. The arrangement therefore permitsofa relatively wide variation in dimensions of certain parts without appreciably varying the contact area. 7 e l 7 When it is desired to actuate the switch device, fluid under pressure is suppliedthrough pipe 53 to piston chamber l4. Since the piston gasket '46 is now in sealing engagement with the seat rib 41, the area of the piston initially ex posed'to this fluid is that within the seat rib 41.

'Therefore, a relatively high initial pressure will berequired-upon thislirnited area to overcome the opposing force exerted by spring 45, but when the seal between gasket and seat rib M is broken,'the full facefof the piston will be exposed'to the pressure of the fluid and the pis- 'ton'will be'thus moved quickly to its extreme left hand position, where its seat rib 49 seals against gasket iill. Bridging contact 'II will therefore be quickly disengaged from the contact tips 24, the action being whatis commonly referred to' as snap action.

As: the lever I2 is first rocked in a clockwise direction, the projection 3flnthereon will swing upwardly and inwardly through a path such thatthe opposition offered by'the spring remains substantially'constant; This will be obvious from noting that 'the moment arm from the center of the aperture 39 to the center of the pin 32', upon which spring 4!! acts, diminishes as the lever I2 is rocked in a clockwise direction, the decrease in effective arm length being very nearly in'proportion to the increase in elongation of the spring. In thismanner the snap action is more positively secured. V 3

Now as the lever l2'rooks in a clockwise direction the lower end swingsthrough'an arc. In order thatthereshall be no binding between the pin '44 and the sleeve 45, the diameter of the aperture'in the sleeve is made somewhat larger than the diameter of the pin 44. The 'full force exertedby the piston l3 in moving to'the left is 7 therefore utilized in'rocking the lever l2.

When'fiuid under pressure supplied to the pis ton chamber is to operate the switch device, is

released, the force exerted by spring 40 will return the bridging contact ll to the position where it bridges the stationary contact tips 24.

If :while'the parts'of the switch 'dvice are in the position shown in Fig. 1 there should. be a leakage of fluid'to piston chamber M for a time and to a degree such that the piston isactuated 'just far enough to disengage gasket 4 6 from seat rib 41, then this fluid may leak past the seat rib j 41 and through the restricted port 52.to the chamber to the left of piston I3 and from thence to the atmosphere by way of a plurality of ports I2, at a rate fast enough to prevent actuation of the piston I3 to its extreme left hand position. In this manner accidental operation of the switch is avoided.

When the piston I3 is in sealing engagement with the gasket 50 it will be noted that the restricted port 52 is disconnected from communication with the atmosphere, so that the pressure of fluid supplied to the piston chamber I I is effective in holding the switch contacts open.

Modification of Fig. 4

Referring now to the modification of Fig. 4, this consists in adding a variable by-pass communication between the portion of piston chamber I4 within the seat rib 41 (inner portion) and the portion exterior of the seat rib (outer portion). This by-pass communication comprises a bushing I4 disposed in an aperture in the cap 5| and having a plurality of radially extending apertures of ports I5 connecting with an axially extending aperture I6. At the lower end of the aperture I6 is a valve abutment 11 formed integrally with a body I8 screwed into the cap 5| and having a bolt head I9 for varying communication between the aperture 16 and a passage leading to the portion of the piston chamber I4 exterior of the seat rib 41.

The purpose of this arrangement is to provide a desired restricted communication between the inner portion of piston chamber I4 and the outer portion so that fluid leaking to the inner portion at a definite rate may at the same rate flow to the outer portion and thus leak through the port 52 to the atmosphere. In this manner accidental operation of the switch device will be avoided.

Modification of Fig. 5

In the embodiment of Fig. 1 the supply of fluid under pressure to the piston chamber I4 actuates the switch device to effect opening of contacts. It may be desirable in some instances to open one set of contacts while closing another set. To provide for this two insulating blocks 34 may be secured to the lever I2, one carrying the aforementioned bridging contact I I and the other carrying a second bridging contact 82. The bridging contact I I may be adapted to bridge the contact tips 24 of two stationary contacts I0 while the bridging contact 82 may be adapted to bridge the contact tips of two difierent stationary contacts, when the lever I2 is rocked in a clockwise direction. Thus one circuit will be opened while the other is closed, the switch thus performing a dual function.

It will be seen from the foregoing description of my invention that I have provided a simply constructed switch which is especially suit-able for operation in connection with brake equipments intended for railway trains and traction vehicles,

and while I have illustrated my invention by several specific constructions, it is not my intention to be limited to the details shown or otherwise than by the spirit and scope of the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. In a pneumatic switch device, in combina tion, a set of contacts, a movable abutment having an inner area and an outer area, means whereby said inner area only is normally exposed to fluid pressure and whereby at a predetermined pressure both said inner and said outer areas become exposed tofluid pressure, and means operated by said abutment for actuating said contacts.

2. In a pneumatic switch device, in combination, a set of contacts, a piston subject to fluid pressure and normally biased to a position where a portion only of its area is exposed to fluid pressure, and being operable at a chosen pressure to be shifted so that its full area is exposed to fluid pressure, and a mechanism operated by said piston for actuating said contacts.

3. In a pneumatic switch device, in combination, a set of contacts, a lever for operating said contacts, a piston for operating said lever, said piston being disposed in a chamber and being operated by supply of fluid under pressure to said chamber, and having a restricted port therein through which fluid supplied to said chamber may escape to the atmosphere, and means whereby when said piston has been shifted to an operating position for cutting off communication between said port and the atmosphere.

4. In a pneumatic switch device, in combination, a set of contacts, means including a piston for operating said contacts, a seat rib, means biasing said piston against said seat rib whereby the area within said seat rib only is exposed to fluid under pressure initially supplied to operate said piston, adjustable means for providing variable degrees of communication for the flow of fluid to the area of said piston outside of said rib, and means for providing a communication to the atmosphere for fluid flowing to said outer area.

5. In a pneumatic switch device, in combination, a set of contacts, a lever for actuating said contacts, a piston operatively connected to said lever, means engaging said piston in a biased position to form an inner chamber to which fluid under pressure is supplied to operate said piston and also forming an outer chamber to which additional area of said piston is exposed, means providing a communication between said inner chamber and said outer chamber, and valve means for controlling the flow of fluid from said inner chamber to said outer chamber.

ELLIS E. HEWITT.

Lil 

